In the known method of aluminothermic rail welding, in which the rail ends, laid with a gap and surrounded by a casting mold, are fused by aluminothermically generated steel and joined to one another, the aluminothermically generated steel serving as weld material should, in its strength properties, correspond as far as possible to the rail steel.
This demand is met in the known aluminothermic mixtures--also called welding portions through addition of alloy elements, such as, in particular, carbon, manganese, vanadium and titanium, to the base mixture consisting of aluminum and iron oxides. For damping and cooling, iron and/or steel scrap are also mixed with the aluminothermic mixture, which simultaneously increases the steel yield.
The preferred rail steels having tensile strengths of from 690 to 880 N/mm.sup.2 have carbon contents of from 0.4 to 0.82% and manganese contents 1 from 0.8 to 1.7% and correspondingly a microstructure which is of predominantly pearlitic form.
DE-C-36 44 106 provides an aluminothermic mixture which ensures the generation of a weld material having an enhanced reproducibility of the composition. This is intended in particular to ensure that the microstructure of the weld material corresponds to the microstructure of the rail material.
This aluminothermic mixture contains additives in the form of homogeneous granules, in particular alloy metals, such as, for example, Mn, Cr, Ni, V and Ti, which can be employed in pure form or as alloys, for example with Fe, damping agents, such as, for example, Fe or Fe alloys, and also carburizing agents, such as carbon or C-containing metals, alloys or carbides.
For the welding of rails, granules consisting of carbon, manganese and iron are added to the mixture in a quantity which ensures the formation of a pearlitic microstructure in the aluminothermically generated steel. Preferably, the granules consist of 1.5 to 3% by weight of carbon, 8 to 12% by weight of manganese and 85 to 90.5% by weight of iron. In some cases, manganese contents of up to 80% are employed.